In welding adjoining work pieces together, such as adjoining flat plates, lengths of pipe or annular objects of various kinds, and in many other situations, especially where a narrow gap is to be filled with metal, the alignment or lateral position of the arc or other heat source, such as electron beam, plasma jet, etc. with respect to a predetermined travel path, must be precisely controlled if a high quality joint is to be produced. Otherwise, inadequate bonding, or faults, burn-throughs, and other flaws may result.
In typical welding operations, the torch or welding instrument is moved along a predetermined main path and, in many cases, is moved in a sinusoidal pattern, i.e., laterally back and forth across the path or gap as it travels along it to insure proper placement of the molten metal being deposited. Maintaining alignment is a problem well recognized and many attempts have been made to solve it, without much success or with complete failure in some cases. With the best of alignment and control devices, it is often difficult or impossible to obtain the high precision control of arc position within a gap that is needed for high quality welding. If the arc or heat source approaches too closely to a wide wall, the wall may be cut or scored deeply, with resulting flaws; if it does not approach close enough, there may be a poor or inadequate bond between the filler metal and the wall.
Many attempts have been made to weld straight line and annular joints by automatic mechanism. Some pipe welding processes and equipment are described in U.S. Pat. Nos. 3,084,246, 3,268,707, 3,737,614, 3,748,433, 2,777,115, 3,646,309, 3,646,311 and others. In the last three patents mentioned, it is proposed to take certain electrical signals from the weld and make use of them to aid in control of certain welding parameters. However, in these cases, the signal is not conditioned for extraction but is merely a continuous wave without timing elements and is not at all suitable for the periodic but systematic control of arc position at critical points in oscillation cycles that is needed in many situations. So far as applicant is aware, none of the prior art proposals using signals from the welding instrument is suitable for controlling lateral oscillation width of the heat source accurately within a narrow gap.
Prior art suggestions have included the use of feelers or other mechanical sensing devices to follow along a groove or gap and help to correct or align the welding instrument with the work or joint. Such sensing devices, in applicant's experience, are often unreliable because spatter of molten metal from an arc, or the presence of foreign particles of any kind, often throw out or disable the sensing device. Moreover, the mechanisms usually proposed are not subject to accurate adjustment and control, even if corrective signals were faithfully obtained and used.
For automatic welding of pipelines, some rather successful processes have become available, including a procedure for first aligning and securing adjoining pipe lengths together internally, as in U.S. Pat. Nos. 3,461,264, 2,561,320, and 3,604,612. U.S. Pat. No. 3,806,694 describes a self-propelled welder apparatus with variable oscillation means, for reasonably good control of the oscillation of the head in pipeline welding. When such devices are used by a skilled attentive operator, excellent results are usually achieved but in the hands of less skilled or inattentive operators, difficulties still arise. A human operator, if not attentive, is not capable of perceiving trends to misalignment or improper oscillation patterns in time to prevent difficulties that can lead quickly to imperfect welds, and with long periods in adverse working conditions, any operator can easily become weary or inattentive.
A particular object of the present invention is to prevent these difficulties and to make it possible to apply corrective devices and procedures to equipment already in service without inordinate costs and complexities. A further object is to make improved procedures available to many types of welding other than pipeline joints, especially joints where narrow and relatively deep gaps are to be filled and properly bonded with filler metal supplied from a consumable electrode, such as fine wire.
The present invention is based on the discovery that by utilizing a generated signal available from a laterally oscillated heat source or probe, etc., and by proper sampling at critical welder instrument positions, corrective action may be indicated or initiated before a trend to misalignment or malposition of the instrument proceeds far enough to cause operating difficulties or weld inperfections.
While signals coming from the heat source, such as arc current, are conveniently used as a basis for the controls of the present process, it is to be understood that other characteristics which vary with lateral position can be used, such as voltage, power (current times voltage), or sound, light, etc., as will be obvious to those skilled in the art after an understanding of the present invention. Other signals or reference values also may be introduced to assist in control of the lateral travel of the instrument or heat source.